Apparatus to reduce the internal frequency of an integrated circuit by detecting a drop in the voltage and frequency

ABSTRACT

A semiconductor integrated circuit is disclosed that operates in synch with a clock signal supplied from an external source, and by a voltage supplied by a power supply. The circuit includes a detection means for detecting that at least one of a frequency of the clock signal and the supply voltage is reduced, and an internal voltage reduction means for lowering an internal voltage of the semiconductor integrated circuit when the detection means detects that at least one of the frequency and the supply voltage is lowered.

This nonprovisional application is a continuation application of andclaims the benefit of International Application No. PCT/JP01/09445,filed Oct. 26, 2001. The disclosure of the prior application is herebyincorporated herein in its entirety by reference.

TECHNICAL FIELD

The present invention generally relates to a semiconductor integratedcircuit device, and electronic apparatuses that include thesemiconductor integrated circuit device, such as a portable apparatus,and particularly relates to technology for reducing power consumption.

BACKGROUND TECHNOLOGY

At present, reduction of power consumption is required of portableapparatuses, such as portable telephones, notebook computer typeapparatuses, and palmtop computer type apparatuses.

FIG. 1 shows an example how a portable apparatus according toconventional technology is configured. The portable apparatus showntherein includes a memory 10 consisting of DRAMs, a DRAM controller 20,an image-processing unit (IP: image processor) 30, a central processingunit (CPU) 40, an interface 50, and a system power circuit 60. The IP 30and the CPU 40 can simultaneously access the memory 10 through the DRAMcontroller 20. That is, the IP 30 and the CPU 40 share a data bus and acommand bus (data/command bus) 70. The IP 30 and the CPU 40 transmit andreceive data to and from an external apparatus, which is notillustrated, through the interface 50 that is connected to an externalI/O terminal.

The CPU 40 controls the system power circuit 60 by a power controlsignal A. The system power circuit 60 supplies power to the internalcircuit of the portable apparatus. In FIG. 1, a power supply path to aperipheral circuit 11 b of a memory core 11 d of the memory 10 isillustrated, for example. When, for example, the portable apparatus isput to a resume mode (stand-by mode, idle status), the CPU 40 outputsthe power control signal A to the system power circuit 60 such that theinternal circuit including the memory 10 is put to a low-power mode. Thememory 10 that is put to the low-power mode is supplied with necessaryminimum power required in order that the peripheral circuit 11 b keepsoperating, and power consumption is reduced.

As mentioned above, the IP 30 and the CPU 40 can simultaneously accessthe memory 10. Accordingly, in order to share the memory 10, the accessrate should be twice as high as the case wherein the IP 30 and the CPU40 independently access the memory 10. For example, when the independentaccess rate of each the IP 30 and the CPU 40 is 50 MHz, in order toshare the memory 10, an access rate of 100 MHz is required.

While simultaneous access is possible, the IP 30 and the CPU 40 do notnecessarily operate (access the memory 10) simultaneously in fact, andoften, only the CPU 40 accesses the memory 10. In other words, theoperating time of the CPU 40 is greater than the operating time of theIP 30. If there are no data that should be processed, the IP 30 does notperform image processing, but is in an idle status.

Even if the IP 30 is in the idle status, the access rate is not changed.In the above-mentioned example, the access rate remains at 100 MHz. Inorder for only the CPU 40 to access the memory 10, the access rate canbe lowered to 50 MHz. That is, when the IP 30 is in the idle status,power is consumed uselessly. Generally, portable apparatuses operate onrechargeable batteries and dry cells. Therefore, if the IP 30 is in theidle status, built-in battery energy is uselessly consumed, and theoperating time of the portable apparatus becomes short.

The problem is similarly applicable to systems that share a memorybetween two or more units and circuits.

THE DISCLOSURE OF THE INVENTION

Accordingly, the general object of the present invention is tocomprehensively solve the above-mentioned problem of the conventionaltechnology.

Specifically, the present invention aims at offering a semiconductorintegrated circuit device, the power consumption of which is reduced, anelectronic apparatus incorporating the semiconductor integrated circuitdevice, and a method of reducing the power consumption.

In order to attain the objects, the semiconductor integrated circuitdevice that operates on a supply voltage provided by a power supply, andin synch with a clock signal provided from outside, according to thepresent invention includes detection means for detecting that at leastone of a frequency of the clock signal and the supply voltage islowered, and means for reducing an internal voltage of the semiconductorintegrated circuit device and/or for delaying operations timing, whenthe detection means detects that at least one of the clock frequency andthe supply voltage is lowered.

The semiconductor integrated circuit device is provided with thedetection means for detecting that at least one of the clock frequencyand the supply voltage is lowered, and carries out operations forautonomously reducing the power consumption, i.e., reducing the internalvoltage of the above-mentioned semiconductor integrated circuit deviceand/or for delaying the operations timing, when the detection meansdetects that at least one of the clock frequency and the supply voltageis lowered. Therefore, power consumption is effectively reduced.

BRIEF EXPLANATION OF THE DRAWINGS

Other objects, features, and advantages of the present invention willbecome still clearer by reading the following explanation with referenceto the attached drawings.

FIG. 1 is a block diagram showing the internal basic configuration of aportable apparatus according to the conventional technology.

FIG. 2 is a block diagram showing a configuration of a first embodimentof the present invention.

FIG. 3 is a circuit diagram showing a configuration example of a circuitarrangement for detecting whether an IP in the configuration of FIG. 2is in an idle status.

FIG. 4 is a circuit diagram showing a configuration example of a supplyvoltage drop detector shown in FIG. 2.

FIG. 5 is a circuit diagram showing a configuration example of a clockfrequency drop detector shown in FIG. 2.

FIG. 6 is a circuit diagram showing a configuration example of an inputbuffer circuit and a pumping circuit shown in FIG. 5.

FIG. 7 is a circuit diagram showing a configuration example of a ringoscillator circuit and the pumping circuit shown in FIG. 5.

FIG. 8 is a circuit diagram showing a configuration example of a voltagecomparator shown in FIG. 5.

FIG. 9 is a circuit diagram showing a configuration example of alow-power mode entry circuit shown in FIG. 2.

FIG. 10 is a circuit diagram showing a configuration example of a timingadjustment circuit shown in FIG. 2.

FIG. 11 is a circuit diagram showing a configuration example of aninternal voltage adjustment circuit shown in FIG. 2.

FIG. 12 is a circuit diagram showing a configuration example of a memorysubstrate voltage adjustment circuit shown in FIG. 2.

FIG. 13 is a timing chart showing operations of the first embodiment ofthe present invention.

FIG. 14 is a block diagram showing the configuration of a secondembodiment of the present invention.

FIG. 15 is a block diagram showing the configuration of a thirdembodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

First, some of the features of the present invention are enumerated asfollows.

The present invention provides means for adjusting the frequency of aclock signal (the system clock signal) of a bus and the like, and meansfor adjusting a voltage provided for system power inside of a memory andthe like. For example, where a system includes two or more informationprocessors, such as a CPU (central processing unit) and an IP (imageprocessor) that access the memory through a common bus, an idle state ofany one of the information processors or a part thereof is detected, andthe frequency of the system clock signal for the memory and theinformation processors is lowered.

Further, when any of the information processors, or a part thereof, isdetermined to be in an idle state, the internal voltage supplied to amemory cell array, a voltage for system power, etc., are reduced.Furthermore, according to the configuration of the present invention,the internal voltage supplied to the memory cell array is furtherreduced by delaying the start timing of reading and writing comparedwith normal operations.

Furthermore, the present invention is configured such that the substratevoltage of the memory is raised when the system power voltage islowered. This is to cope with the situation wherein the threshold oftransistors, especially NMOS transistors, in the memory is raised whenthe system power voltage is lowered.

Hereafter, preferred embodiments that realize the above-describedfeatures are explained in detail referring to the attached drawings.

The First Embodiment

The first of the preferred embodiments of the present invention isexplained in detail referring to the attached drawings.

FIG. 2 is a block diagram showing the first embodiment of the presentinvention, which drawing shows the configuration of a semiconductorintegrated circuit device, and an electronic apparatus incorporating thesemiconductor integrated circuit device.

The electronic apparatus of the first embodiment shown in FIG. 2includes a memory 100 consisting of memory devices, such as SDRAM(synchronous type DRAM), a DRAM controller 200, a control unit 800, aninterface 500, and a system power circuit 600. The electronic apparatusis equivalent to, for example, a card that is provided with these partson a circuit board; and a cellular phone, a personal computer, and thelike that are provided with these parts, and a circuit board. The memory100 is an example of the semiconductor integrated circuit device of thepresent invention. The control unit 800 includes an image processor (IP)300, a CPU 400, and a clock generator 700. The IP 300 and the CPU 400share the memory 100 through a data command bus 900 and the DRAMcontroller 200. The clock generator 700 supplies a system clock signalto the memory 100.

One of the features of the embodiment is lowering the frequency of thesystem clock signal and the supply voltage that are provided to thememory 100, when the IP 300 is in the idle status. Another feature ofthe embodiment is that the memory 100 detects the drop of the frequencyof the system clock signal and the drop of the supply voltage, andautonomously shifts to a low-power operation mode.

Hereafter, the embodiment is explained in detail.

Lowering/Resuming the System Power/System Clock Signal Frequency

According to the embodiment, lowering the system clock signal frequencyand the system power voltage, and resuming the system clock signalfrequency and the system power voltage for normal operations arecontrolled by a signal that is output from the CPU 400.

That is, when lowering the system power voltage and the system clocksignal frequency, for example, the CPU 400 outputs a power controlsignal B to the system power circuit 600, and outputs a clock controlsignal D to the clock generator 700. When the power control signal B isinput, the system power circuit 600 changes the system power voltage toa lower voltage by a predetermined amount. Further, when the clockcontrol signal D is input, the clock generator 700 changes the systemclock signal frequency to a predetermined clock frequency, for example,half of the frequency used in normal operations.

Here, the system power circuit 600 is a circuit that supplies a supplyvoltage to each part of the electronic apparatus, and the clockgenerator 700 is a circuit that supplies the system clock signal to theinternal circuit of the memory 100, and others.

Further, when resuming the system power voltage for normal operations,the CPU 400 outputs a power control signal A to the system power circuit600, and outputs a clock control signal C to the clock generator 700.The system power circuit 600 changes the system power voltage to thevoltage for normal operations, when the power control signal A is input.Further, the clock generator 700 changes the system clock signal to theclock frequency for normal operations when the clock control signal C isinput.

Further, the system clock signal may be lowered by a configurationwherein a voltage applied to a crystal oscillator contained in the clockgenerator 700 is changed, and by a configuration wherein a divider (suchas a programmable divider) is provided to the output stage of the clockgenerator 700, and the dividing ratio is changed. Here, when thedividing ratio of the divider provided to the output stage of the clockgenerator 700 is changed, the clock control signals C and D output fromthe CPU 400 are input to this divider.

Further, when reducing the system clock signal, the operation clock ofthe CPU 400 can be maintained or adjusted to a predetermined operationclock by adjusting a step-up ratio of a step-up circuit of the CPU 400.

Further, according to the embodiment, the change of the system powervoltage and the system clock signal frequency is performed based onwhether the IP 300 is operating, or in an idle state. That is, accordingto the embodiment, when the IP 300 is in operation, the system powervoltage and the system clock signal frequency are set at values fornormal operations, and when the IP 300 is in the idle state, the systempower voltage and the system clock signal frequency are lowered from thenormal operations values.

Detection of the Operating State/Idle State of the IP 300

The CPU 400 determines whether the IP 300 is in the operating state orin the idle state. This is realized by one of the followingconfigurations, namely (1) the CPU 400 always or periodically (everypredetermined cycle) polls the IP 300 for detecting whether the IP 300is operating or idle; (2) the IP 300 periodically outputs apredetermined signal (IP operating signal/IP idle signal) to the CPU 400while operating/being idle, respectively; and (3) whenever the IP 300shifts to the idle state from the operating state, and whenever itshifts to the operating state from the idle state, predeterminedcorresponding signals are output to the CPU 400. Nevertheless, theconfiguration is not limited to what is described above, but any othervariation may be employed as long as the configuration enables the CPU400 to detect whether the IP 300 is in operation or in the idle status.

FIG. 3 shows an example of the configuration for detecting the operatingstate/idle state of the IP 300. The IP idle state detector shown by FIG.3 includes a NAND gate 801 and an inverter 802 that are provided betweenthe IP 300 and the CPU 400. The IP 300 always outputs an IP idle signalduring the period while the IP 300 is in idle state (high level, orlogic 1). While the IP idle signal is output, the output of the NANDgate 801 changes according to the system clock signal, and is suppliedto the CPU 400 through the inverter 802. That is, while the IP idlesignal is output, the system clock signal continues being supplied tothe CPU 400. In this manner, the CPU 400 detects the idle state of theIP 300.

The Change of the Memory Operation Mode

Further, according to the embodiment, when the idle state of the IP 300is detected as mentioned above, the memory 100 is changed from thenormal operation mode to a low-power mode wherein the memory operates atlow power. Accordingly, with this embodiment, the power consumption isfurther reduced. In the following, the case where the change isperformed based on detection means prepared in the memory 100 isexplained as an example.

The detection means is for detecting the system clock signal frequencybeing lowered, and the system power voltage being reduced. That is,according to the embodiment, when the CPU 400 detects that the IP 300enters the idle state, the system power voltage and the system clocksignal frequency are lowered, which are then detected by the detectionmeans (equivalent to the supply voltage drop detector 114 and the clockfrequency drop detector 115 in FIG. 2) provided in the memory 100, andeach circuit (120, 130, and 140) is made to enter the low-power mode.

Hereafter, each circuit is explained in detail referring to the attacheddrawings.

Supply Voltage Drop Detector 114

First, examples of the configuration and circuit arrangement of thesupply voltage drop detector 114 shown by FIG. 2 are explained in detailwith reference to sections (a) and (b), respectively, of FIG. 4.

At the section (a) of FIG. 4, an example of a block diagram of thesupply voltage drop detector 114 is shown, wherein the system powervoltage and an external reference voltage Vref are provided to thesupply voltage drop detector 114. Further, an example of the circuitarrangement of the supply voltage drop detector 114 is shown at (b) ofFIG. 4. As shown at (b) of FIG. 4, the supply voltage detector 114includes a differential amplifying circuit 114-1, and a current mirrorcircuit (NMOS transistor) 114-2 serving as a load resistance. In thismanner, the supply voltage drop detector 114 of the embodiment outputs asupply voltage drop detection signal when the system power voltagebecomes lower than a predetermined voltage. It is preferred that athreshold voltage be set to the gate of the NMOS transistor 114-2, towhich Vref is provided, and the supply voltage drop detection signal beoutput when the system power voltage becomes lower than Vref by anamount equal to the threshold voltage.

Further, as shown by FIG. 4, the supply voltage drop detector 114includes a PMOS 114-3 on the source side (GND side) of the differentialamplifying circuit 114-1, and an inverted memory-access signal isprovided to the gate of the PMOS transistor 114-3. In this manner, onlywhen the memory-access signal is input, the supply voltage drop detector114 is made to operate. That is, the supply voltage drop detector 114operates only when required, reducing the power consumption.

Clock Frequency Drop Detector 115

Next, the circuit arrangement of the clock frequency drop detector 115shown by FIG. 2 is explained in detail in reference to FIGS. 5 through8.

FIG. 5 is a block diagram showing a configuration example of the clockfrequency drop detector 115. As shown by FIG. 5, the clock frequencydrop detector 115 detects whether the system clock signal frequency islowered by making the memory-access signal a trigger, and the clockfrequency drop detection signal is output when it is determined that thesystem clock signal frequency is lowered.

In reference to FIGS. 5 through 8, in the clock frequency drop detector115, the system clock signal that is input is buffer-processed,including delay, by an input-buffer circuit 115-1 (FIG. 6), and isconverted into a direct current voltage by a pumping circuit (chargepump circuit) 115-2 according to the clock frequency (i.e., a capacitorC1 shown in FIG. 6 is charged). The voltage (a) shown in FIG. 5 and FIG.6 of the capacitor C1 is provided to the gate of an NMOS transistor115-51 a (FIG. 8) of a differential amplifying circuit 115-51 of avoltage comparator 115-5 shown in FIG. 5 and FIG. 8. Further, a signalgenerator 115-3 shown in FIG. 5 and FIG. 7 outputs a signal of apredetermined frequency based on the memory-access signal that is input.The signal of the predetermined frequency is input to a pumping circuit(charge pump circuit) 115-4, and is converted to a direct currentvoltage according to the frequency (i.e., a capacitor C2 shown in FIG. 7is charged). A voltage (b), which is shown in FIG. 5 and FIG. 7, of thecapacitor C2 is provided to the gate of an NMOS transistor 115-51 b(FIG. 8) of the differential amplifying circuit 115-51 of the voltagecomparator 115-5.

Here, the differential amplifying circuit 115-51 includes a currentmirror circuit 115-52 consisting of NMOS transistors, the gates of whichare connected to the drain side of an NMOS transistor 115-51 b, themirror circuit 115-52 serving as a load resistance. In this manner, thevoltage comparator 115-5 shown in FIG. 8 determines whether the systemclock signal frequency is lowered, only when a direct current voltage(b) is provided to the gate of the NMOS transistor 115-51 b.

Furthermore, the voltage comparator 115-5 includes an NMOS transistor115-53 on the source side (GND side) of the differential amplifyingcircuit 115-1. To the gate of the NMOS transistor 115-13, thememory-access signal is provided. Only when the memory-access signal isinput, the clock frequency drop detection signal is output.

Low-Power Mode Entry Circuit 116

The supply voltage drop detection signal output from the supply voltagedrop detector 114 and the clock frequency drop detection signal outputfrom and the clock frequency drop detector 115 are provided to alow-power mode entry circuit 116 shown in FIG. 2. In the following, aconfiguration example of the low-power mode entry circuit 116 and anexample of operations are explained with reference to FIG. 9.

As shown in FIG. 9, the low-power mode entry circuit 116 according tothe embodiment includes NAND gates 116-1 and 116-2. When both the clockfrequency drop detection signal and the supply voltage drop detectionsignal are input, a low-power mode entry signal is output through abuffer circuit 116-3.

Further, the example shown in FIG. 9 is configured such that thememory-access signal is also input, without which the low-power modeentry signal is not output. In this manner, when there is no access tothe memory, the low-power mode entry signal is prevented from beingoutput, and useless power consumption is avoided.

Timing Adjustment Circuit 120

A configuration example of a timing adjustment circuit 120 that operatesbased on the low-power mode entry signal that is output as describedabove is explained with reference to the circuit diagram of FIG. 10.

The timing adjustment circuit 120 includes a buffer circuit 120-1, NANDgates 120-2, and 120-3, a NOR gate 120-4, and an inverter 120-5. Whenthe low-power mode entry signal is input; the timing adjustment circuit120 outputs a timing adjustment signal for delaying the timing ofinternal operations of the memory 100. In the case of the example shownin FIG. 10, a buffer circuit 120-1 consisting of an odd number ofinverters is further included for delaying the memory-access signal by apredetermined period. In this manner, a signal for adjusting timing(timing adjustment signal) is generated at a desired timing.

By providing the timing adjustment circuit 120, the embodiment canfurther reduce the internal voltage supplied to a word line selectiondrive circuit 101 c (FIG. 2).

Internal Voltage Adjustment Circuit 130

Next, a configuration example of an internal voltage adjustment circuit130 that also operates based on the low-power mode entry signal isexplained with reference to the circuit diagram of FIG. 11.

The internal voltage adjustment circuit 130 shown in FIG. 11 includes atransistor circuit 130-1 consisting of a PMOS transistor and an NMOStransistor. The low-power mode entry signal is provided to the gate ofthe two transistors. When the low-power mode entry signal is provided,the NMOS transistor is turned on and the PMOS transistor is turned off.The PMOS transistor has a drive capacity higher than the NMOStransistor. Accordingly, when the PMOS transistor is turned on (i.e.,normal operations), an internal voltage Vpp is supplied to the memorycore almost as it is. On the other hand, when the NMOS transistor isturned on (i.e., at the time of entering the low-power mode), aninternal voltage lower than at the time of normal operations is suppliedto the memory core.

Accordingly, by providing the internal voltage adjustment circuit 130,the supply voltage provided to the memory 100, while a high-speedoperation is not required because the IP 300 is in the idle status, islowered, and power consumption is reduced.

Memory Substrate Voltage Adjustment Circuit 140

Next, a memory substrate voltage adjustment circuit 140 according to theembodiment is explained.

In this embodiment, the memory substrate voltage adjustment circuit 140is a circuit for raising the substrate voltage VBB in the low-power modeoperations.

Generally, when the supply voltage to the memory is lowered in thelow-power mode operations, the problem is that the required thresholdvoltage of the NMOS transistor becomes high, especially when thesubstrate bias is set pursuant to conventional practices. Accordingly,the memory substrate voltage adjustment circuit 140 is provided in orderto solve this problem.

An example of the circuit arrangement of the memory substrate voltageadjustment circuit 140 is shown in FIG. 12. With reference to FIG. 12,the memory substrate voltage adjustment circuit 140 includes a pluralityof NMOS transistors 140-2 through 140-5 connected in series (a four-stepconfiguration), and an NMOS transistor 140-1 connected in parallel withthe NMOS transistor on the side of VSS. The low-power mode entry signalis provided to the gate of the NMOS transistor 140-1. When the NMOStransistor 140-1 is turned on, the four-step configuration of the NMOStransistors between VSS-VBB serves as a three-step configuration. Inthis manner, the substrate voltage VBB is raised.

Further, the configuration of the memory substrate voltage adjustmentcircuit 140 shown in FIG. 12 is capable of quickly resuming thesubstrate voltage VBB for the normal operations when the low-power modeentry signal is not provided, or when the low-power mode entry signal isremoved.

Timing Chart in Normal Operation Mode and Low Power Operation Mode

Next, waveforms of each signal for normal mode operations and low-powermode operations are explained with reference to FIG. 13. The followingexplanation describes the case where the operation mode is changed tothe low-power mode when both the system power voltage and the systemclock signal frequency are lowered.

When the IP 300 outputs an IP idle signal, then the CPU 400 determinesthat the IP 300 is in the idle state, and lowers the power supply powercontrol signal A, and raises the power supply power control signal B,such that the system power voltage is reduced as shown in FIG. 13.Further, similarly, the CPU 400 lowers the clock frequency of the systemclock signal by bringing down the clock control signal C, and by raisingthe power supply power control signal B. FIG. 13 shows an examplewherein the clock frequency of the system clock signal frequency islowered to one half.

As described above, the supply voltage drop detector 114 and the clockfrequency drop detector 115 detect the system power voltage and thesystem clock signal frequency, respectively, being lowered, and thelow-power mode entry signal is output from the low-power mode entrycircuit 116.

Here, the internal voltage Vpp output from the internal voltageadjustment circuit 130, where the low-power mode entry signal is input,is lower than the internal voltage Vpp in the normal operation mode. Forthis reason, a voltage (WL A2) provided to a word line (word line of thememory cell array 101 a shown in FIG. 2) that is based on the reducedinternal voltage Vpp is also lowered as compared with a voltage (WL A1)that is provided in the normal mode operations as shown in FIG. 13.Similarly, a voltage (BL A2) provided to a bit line in the low-powermode operations is lowered as compared with a voltage (BL A1) providedin the normal mode operations as shown in FIG. 13.

The above explanation is in reference to changing the operation mode tothe low-power mode. Resuming the normal operation mode is realized asfollows. The CPU 400 detects that the IP 300 starts operating, based onwhich the system power voltage and the system clock signal frequency arereturned to the values for the normal operations. The resumption isdetected by the supply voltage drop detector 114 and the clock frequencydrop detector 115, based on which the low-power mode entry signal thatis output from the low-power mode entry circuit 116 is suspended.

As described above, the present embodiment not only lowers the systempower voltage, but also changes the operation mode of the memory 100from the normal operation mode to the low-power operation mode when theIP 300 is in the idle state, and operations are carried out with minimumrequired power consumption.

Furthermore, according to the present embodiment, the timing ofread-out/writing from/to the memory cell array 101 a is adjusted so thatthe internal voltage Vpp is further reduced, realizing reduction of thepower consumption.

Further, according to the present embodiment, the substrate voltage VBBis raised in order to solve the problem wherein the threshold of thetransistor on the memory substrate, especially a NMOS transistor, goesup due to the lower system power voltage.

In the above, the first embodiment of the present invention isexplained. In summary, the configuration is such that both the operatingvoltage and the system clock signal frequency (timing of operations) ofthe memory 100 are lowered when the memory 100 detects that the IP 300is in the idle state. Nevertheless, the configuration may theoreticallybe such that only one of the operating voltage and the system clocksignal frequency is lowered.

Further, although the first embodiment as described above is constitutedsuch that the CPU 400 and the IP 300 access the memory 100 (moreaccurately put, access the DRAM controller 200 for controllingtransmission to and reception of data from the memory 100) through thesame bus 900, the present invention is not limited to this configurationbut can be applied to any system where two or more informationprocessors use the same bus.

Furthermore, although the memory 100 is described as SDRAM, memory ofother types can be used.

The Second Embodiment

Next, the second embodiment, of the present invention is explained.

In the case of the first embodiment, the change of the operation mode ofthe memory 100 to the low power mode is based on the detection result ofthe detection means (the supply voltage drop detector 114 and the clockfrequency drop detector 115) prepared in the memory 100. In contrast,according to the second embodiment of the present invention, this changeis carried out based on a command that is output from the CPU 400.

The Change of the Operation Mode of Memory 100A

FIG. 14 is a block diagram showing a configuration example according tothe second embodiment.

With reference to FIG. 14, when the idle state of the IP 300 isdetected, the CPU 400 provides an entry command for changing to the lowpower operation mode (henceforth the low-power mode entry command) to amemory 100A through the DRAM controller 200. Here, the configuration andthe method for detecting the idle state of the IP 300 are the same asthose of the first embodiment. Further, an address code (hereaftercalled the target circuit address code) that indicates which of thecircuits (in FIG. 14, the timing adjustment circuit 120, the internalvoltage adjustment circuit 130, and the memory substrate voltageadjustment circuit 140, hereafter abbreviated as “120, 130, and 140”)are to be set for the low power operation mode is also provided to thememory 100A from the CPU 400.

The low-power mode entry command and the target circuit address codeprovided to the memory 100A are then provided to an operation modeoutput circuit 111. The operation mode output circuit 111 includes acommand decoder and an address buffer.

According to this configuration, the low-power mode entry commandprovided by the CPU 400 is decoded by the command decoder, and isprovided to a mode register 112 that is prepared in the later stage.Further, the target circuit address code provided by the CPU 400 is thenprovided to an address buffer, is converted into an address (henceforththe target circuit address) assigned to the target circuits (120, 130,and 140) of the memory 100A, and is provided to the mode register 112with the low-power mode entry command that is decoded (henceforth calledthe low power operation mode set command).

The mode register 112 holds the operation mode set to each circuit (120,130, and 140) of the memory 100A. In this manner, the low-power modeoperation set command provided by the operation mode output circuit 111is set to the address corresponding to the target circuit address of themode register 112.

Further, if any of the circuits (120, 130, and 140) (target circuit) isset to the low-power mode operation by the mode register 112, anindividual circuit low-power mode entry circuit 113 outputs a low-powermode entry signal to the corresponding target circuit. Here, thedetection of the operation mode of each circuit (120, 130, and 140) bythe individual circuit low-power mode entry circuit 113 can also berealized by configuring so that the individual circuit low-power modeentry circuit 113 continuously or periodically refers to the moderegister 112, or by configuring so that a predetermined signal is outputto the individual circuit low-power mode entry circuit 113 from the moderegister 112 whenever the setup in the mode register 112 is updated.Nevertheless, the configuration can be modified as long as it ispossible to detect the operation mode that the individual circuitlow-power mode entry circuit 113 sets to each of the circuits (120, 130,and 140).

According to the configuration described above, the individual circuitlow-power mode entry circuit 113 outputs the individual circuitlow-power mode entry signal to the corresponding circuit (120, 130, and140), according to the set-up in the mode register 112 of the low-powermode operations for each of the circuits (120, 130, and 140). In thismanner, the circuits (120, 130, and 140) reduce power consumption, ifthe individual circuit low-power mode entry signal is provided.

Since the configuration and operations of the timing adjustment circuit120, the internals voltage adjustment circuit 130, and the memorysubstrate voltage adjustment circuit 140 are the same as those describedin reference to the first embodiment, explanations are omitted here.However, in the second embodiment, the individual circuit low-power modeentry signal is provided to each of the circuits (120, 130, and 140).

Further, although the above-mentioned explanation is about changing theoperation mode to the low power operation mode, changing the operationmode to the normal operation mode is carried out in a manner similar tothe above with the individual circuit low-power mode entry command beingreplaced with an individual circuit normal mode entry command (a commandfor changing to the normal operation mode for each circuit).

As described above, like the first embodiment, the second embodiment ofthe present invention realizes operations with minimum required powerconsumption by preparing the normal operation mode and the low poweroperation mode.

Furthermore, according to the present embodiment, the timing ofread-out/writing from/to the memory cell array 101 a is adjusted, and inthis manner, further reduction of the internal voltage Vpp is realized,reducing the power consumption.

Further, according to the present embodiment, the substrate voltage VBBis raised so that the problem due to the threshold of the transistor onthe memory substrate, especially a NMOS transistor, being raisedcorresponding to the drop of the system power voltage is solved.

Further, since the operation mode is changed by the command according tothe present embodiment, an advantage that the operation mode can beindividually set to each of the circuits (120, 130, and 140) isrealized.

Furthermore, since the operation mode is changed by the commandaccording to the present embodiment, even when a circuit (such as anLSI) that is asynchronous to the system clock signal is included in theelectronic apparatus, entering the power consumption operation mode canbe carried out, and reduction of the power consumption is realized. Thatis, even when the memory 100A in FIG. 14, for example, operatesasynchronously to the system clock signal, reduction of the powerconsumption by the memory 100A is realized by using the command.

The Third Embodiment

Next, the third embodiment of the present invention is explained withreference to the attached drawings.

FIG. 15 is a block diagram showing the configuration of the thirdembodiment of the present invention. As shown by FIG. 15, the presentembodiment is configured such that the change of the operation mode isperformed based on the detection result of the clock frequency dropdetector 115. Here, the clock frequency drop detector 115 shown in FIG.15 is the same as described in reference to the first embodiment.

Accordingly, when the CPU 400 detects that the IP 300 is in the idlestate, and the system clock signal frequency is lowered, the clockfrequency drop detector 115 detects the idle state, and the clockfrequency drop detection signal is provided to the low-power mode entrycircuit 117 that is prepared in a later stage.

Further, when the clock frequency drop detection signal is input, thelow-power mode entry circuit 117 outputs the low-power mode entry signalto the timing adjustment circuit 120 that is prepared in the laterstage, and makes a memory 100B operate in the low power operation mode.

Further, according to the present embodiment, the low-power mode entrycircuit 117 is connected to the IP 300 and the CPU 400 through the DRAMcontroller 200, as shown in FIG. 15. In this manner, according to thepresent embodiment, based on the input provided by the IP 300 or the CPU400, (1) the memory 100B is shifted to the low power operation mode, (2)the memory returns from the low power operation mode, and (3) the shiftto the low power operation mode is restricted.

For example, (1) in order to shift to the low power operation mode basedon an input provided by the IP 300 or the CPU 400, the IP 300 maydirectly provide the signal for shifting to the low power operation modeto the low-power mode entry circuit 117 through the DRAM controller 200when the IP 300 becomes idle, or the CPU 400 upon detecting the idlestate of the IP 300 may provide the signal for shifting to the low poweroperation mode.

Further, (2) when returning from the low power operation mode, theconfiguration that is same as (1) above serves the purpose. Here, inthis case, the signal output from the IP 300 or the CPU 400 is a signalfor returning to the normal operation mode.

Further, in the cases of (1) and (2) above, the configuration can beeither such that the operation mode is changed only when the clockfrequency drop detection signal is input, or such that the operationmode is changed regardless of the presence of the clock frequency dropdetection signal.

Further, (3) restriction of the shift to the low power operation mode isrealized by providing a flag for indicating permission/disapproval ofthe shift to the low power operation mode in the low-power mode entrycircuit 117, for example. When the CPU 400 allows the shift, the flagfor permission is stored to the low-power mode entry circuit 117; andwhen the shift is not allowed, the flag for disapproval is stored.Accordingly, the low-power mode entry circuit 117 outputs the low-powermode entry signal when a clock frequency drop detection signal is inputon the condition that the permission flag is stored. Further, in thiscase, the configuration can be such that the CPU 400 sets the flagaccording to directions that an outside apparatus provides through theinterface 500.

Further, if the low-power mode entry circuit 117 provides the low-powermode entry signal, the timing adjustment circuit 120 outputs the timingadjustment signal. Further, the internal voltage generating circuit 150provides the internal voltage Vpp to the word line selection drivecircuit 101 c at the timing based on the timing adjustment signal thatis input. Further, when the timing adjustment signal is input in thismanner, the internal voltage generating circuit 150 outputs a voltagethat is lower than the internal voltage Vpp of the normal operationmode.

Thus, according to the present embodiment, since the internal voltage islowered while adjusting the timing of read-out/writing from/to thememory cell array 101 a, the power consumption is further loweredcompared to the case wherein only the system clock signal frequency islowered.

Other Embodiments

The preferred embodiments are described above, wherein the powerconsumption is reduced by lowering the system power voltage, by loweringthe system clock signal, and by reducing the power consumption of thememory. However, the present invention is not limited to theseembodiments, but rather, various modifications and implementationswithout deviating from the scope of the present invention areconceivable.

1. A memory semiconductor integrated circuit that operates in synch witha clock signal that is provided from outside, and based on a supplyvoltage provided by a power source, comprising: a voltage drop detectionunit configured to output a voltage drop detection signal in response tothe supply voltage dropping below a predetermined voltage; a clockfrequency drop detection unit configured to output a frequency dropdetection signal in response to a frequency of the clock signal droppingbelow a predetermined frequency; and an internal voltage reduction unitconfigured to reduce an internal voltage of said semiconductorintegrated circuit in response to at least one of the voltage dropdetection signal and the clock frequency drop detection signal.
 2. Amemory circuit that operates in synch with a clock signal that isprovided from outside and based on a supply voltage provided by a powersource, comprising: a voltage drop detection unit configured to output avoltage drop detection signal in response to the supply voltage droppingbelow a predetermined voltage; and a clock frequency drop detection unitconfigured to output a frequency drop detection signal in response to afrequency of the clock signal dropping below a predetermined frequency;and a timing adjustment unit configured to supply, to an internalcircuit of the memory circuit, a timing adjustment signal for delayingtiming of internal operations of the memory circuit in response to atleast one of the voltage drop detection signal and the frequency dropdetection signal.
 3. A memory circuit that operates based on a supplyvoltage provided by a power source, comprising: a voltage drop detectionunit configured to output a voltage drop detection signal in response tothe supply voltage dropping below a predetermined voltage; a clockfrequency drop detection trait configured to output a frequency dropdetection signal in response to a frequency of the clock signal droppingbelow a predetermined frequency; and a substrate voltage increasing unitconfigured to increase, in response to at least one of the frequencydrop detection signal and the voltage drop detection signal, a voltageprovided to a substrate on which said semiconductor integrated circuitsis mounted by a predetermined amount.